How Hidden Dams Stop Rain from Killing People
Rain is the lifeblood of our planet and sometimes it can be our worst enemy Countless drivers under seige by an onslaught of water Our battle against flooding has transformed cities over centuries into highways for water But this solution created new and deadly problems that we didn’t expect And so we built these Prisons but not for people But how does this stop flooding and why have we built hundreds of them? Some are massive like this dam and others, hidden in plain sight To understand why we built these we’ll go on a journey to uncover how we went from water highways to water prisons From Toronto to Tokyo to explore why the Japanese built apartments designed to flood spent $2 billion dollars on an underground storage facility and more importantly what this means for the future of flooding in all our cities Lets go This video is brought to you by Brilliant more on them later We’ve been dealing with rain for a long time But it wasn’t until until ancient Rome where rain could cause big problems You see in natural settings most of the rain would evaporate or soak into the soil with only a small amount running off the surface But Rome is far from natural with its hard streets and buildings The result is as much as 5.5x more rain running off which can flood low lying areas if its not dealt with And so the first major sewer was born Completed in 2 BC and you can still see it today The 3.2km long Cloaca Maxima or “Greatest Sewer” was the answer It took rain off streets using drainage trenches and moved millions of liters of water into the river far more than in the past This was the height of sewer tech for a long time as Rome would fall plunging cities and technology into the dark ages But eventually things got better And we’re now in 19th century London and it’s become a bustling metropolis Factories are everywhere and people are flocking to the city for jobs London's population has exploded from 750,000 in 1780 to a staggering 3 million in only 80 years and with that comes a lot more stormwater to remove By 1856 London’s sewer network spanned hundreds of kilometers far exceeding the Roman Empire Many of these sewers lines are way bigger than the Cloaca Maxima And they exit into the Thames River through a series of outfalls This is way more water to manage and the sewer system faces a new problem THPPTPHTPHPHHPH An amazing invention called the water closet became widely available Ohhhhhhohohohohohoh And by the 1800s over 250 million liters of wastewater were pouring into sewers daily and could cause serious blockages that would backup water into your home and when it rained… Disaster entire neighborhoods would be flooded London needed help and the solution involved a massive and complex sewer project that's too big for this video But we can dive into one important discovery: AHHHHHHHHHHHHHHH THHHHHEEE SPEEEEEEEEEED Speed was the cause of blockages as this engineering guide pointed out Many sewers had large flat bottoms that under low water levels created a lot of friction that slowed down the flow of wastewater causing sediment to be deposited until sewers Eugh Better engineering fixed this First no more flat bottoms Egg-shaped sewers were built to concentrate and reduce friction during low flow to keep everything moving And also: The Speeeeeeeed Grady from Practical Engineering had a great demo showing how increasing the slope increases speed and would sweep out debris And so, many experiments were done to find the eventually this “self-cleansing” knowledge saved London from blockages and flooding And kicked off the speed revolution in sewers [Jingle - Speed Racer] This egg-shaped sewer tech made its way over to my city and over time faster and faster water removal became the way growing cities including my own were protected against flooding Over decades Toronto was transformed into a racetrack for rain And it starts by angling properties and paved streets so that water flows directly and quickly into sewer inlets In newer parts of the city poop pipes are now separate from stormwater pipes which minimizes the blockages that plagued London We could then use concrete pipes that are larger smoother and better aligned speeding things up even further The rivers that received this water were also improved Before there would be twists and turns but these were too slow and hindered water movement during heavy rain causing water levels to rise And so, we straightened and widened them in massive infrastructure projects The result? Toronto can now dump more water into the river without flooding the surrounding area.
But that’s not all we paved some rivers with concrete which let even more water flow And I want to show you the impact of this network when it rains so we’re here at Black Creek Flood Control Channel This is 4km of concrete highway that cuts across major residential areas and protects them from flooding There’s a second channel cut here for low flow and do you remember why we did this? It’s the egg shaped sewer all over again this concentrates water to maintain the self cleansing velocity Without it the speed would be halved and we can calculate this through the manning formula which estimates water velocity The variable changed here is the hydraulic radius which compares volume against how much surface area it touches and in the flat channel it’s 10 times more which slows down flow, and now you know the science behind it. I’m not an engineer and interpreting this equation for this video was hard and it took soo many hours to figure out Same during the research for this video Occasionally I skipped topics because of time or I had to rely on an author’s conclusions and that’s often because my math and analytical skills weren’t good enough I hate that I want to know how it works myself and I bet you are the same So I’m learning calculus and statistics using Brilliant.org which uses interactive and clever lessons to help me truly understand a concept like their course on Statistics Fundamentals It shows how data can be deceiving and teaches me how to think more critically so I can spot potential inaccuracies in articles and papers I come across Brilliant has thousands of lessons from foundational and advanced math, computer science, neural networks, and more with new ones added monthly. Each lesson is also bite sized so I can squeeze them into increasingly smaller gaps in my schedule no matter where I go As an educational creator I love that Brilliant doesn’t waste my time I know what good content is and Brilliant has done a lot to ensure their lessons are clear, concise and fun Doing one feels a lot like being at a science center So if you're a lifelong learner like me or want to develop technical skills to level up your career head over to Brilliant.org/AndrewLam
or click the link in the description below You have a full 30 days to try every course for free and see if it’s a fit for you Plus the first 200 of you to sign up will get 20% off their annual subscription Let’s get back to showing you how a channel transforms into a water highway when it rains Today it’s calm, serene and there’s only a trickle of water in here which is why we can walk over to this depth marker that measures the height of the water in here Over there is a camera that films this 24 hours a day and stats are recorded of the height of the water in this channel which is critical to alert residents of any flood risk On a day with light rain the bottom here is completely filled in less than 45 minutes from rainwater I really wanted to go down there but I know one slip And that’s it That water You’re not coming back from that That’s..that’s it But don't worry This means the sewer system and the speed is protecting our city right? THEEEE SPEEEEEEEED That’s why people were calm as Hurricane Hazel was raging towards Toronto in 1954 The day before the local newspaper didn’t think much of it ehhhhh just some minor flooding and heavy rain Overnight, the storm struck and by the next day everything changed Drownings, fallen trees, crushed homes and washed out bridges Some rivers ran as much as 16ft above their normal levels Much of the destruction was around rivers as it swelled and washed away roads, bridges, and buildings I’m standing at one such location This is Raymore Road or it used to be It had 14 homes along the peninsula section here During the storm the humber river rose and washed away all those houses killing 35 And it’s never been rebuilt instead being turned into a park and a memorial In total Hurricane Hazel killed 81 across the province as the storm stalled over Toronto unleashing 8 inches of rain But like all great cities Toronto rose up, fixed the damage andddd… started looking for someone to blame, turns out… We caused it We underestimated the power of nature like the humber river and it doesn't look big here But zoom out here’s where I am and we find the river connects to 1800km of waterways that drains 911 square kilometers of land It’s massive and during hazel the storm paused on top of all of this and rain was funneled downstream like a snowball rolling downhill until it all arrives here sweeping away homes and washing away bridges Speed was the solution and now the water running into the river has made the problem even worse Figuring out how to fix this took three years and in 1959 Toronto had a bold new plan One part was the Flood Control Works Program Toronto built infrastructure like the Claireville dam to reduce the power of rivers Its job is to keep rainwater out of Toronto and lets see how The before and after shots gives a good overview a winding river was turned into a prison complex for rain It does this by trapping and releasing water using massive floodgates and is controlled through a monitoring station that upon detecting a big storm can open the gates and drain the reservoir as needed to make room for more water The gates then partially close and the dam will hold back most of the rain coming down and prevent it from reaching Toronto When the storm passes the gates can open and water safely released into a much calmer river Toronto built several of these dams and greatly reducing flooding The other part of the plan was the Lands Acquisition Program This may be obvious now but building and living on floodplains wasn't the brightest idea especially as urbanization changed how high and how much area rivers will flood And so, a regulatory body called the TRCA was created they bought up threatened homes turned them into parks and protected them from shortsighted developers Since then no one has died by their home being swept away by water in Toronto Congrats right? Absolutely! And sewers are still being overwhelmed in big storms causing huge damage but we can’t put a dam in your street so we needed something different The solution is right here [Angels Singing] hidden in plain sight Disguised as your friendly neighborhood soccer field There are two things that make this place a little unusual First off this soccer field is in a really deep pit Wwwwaahhhhhh Mmmm woooo That goes really far down And that’s not the only unusual thing about this pit But also this structure beside me and on the opposite side of the field These are water inlets and outlets and the secret to turning this soccer pit into a prison for water called a dry retention pond During heavy rain water will overflow a nearby underground weir and will travel down a pipe into the park And enter through these inlets where the rocks break up its energy and water will fill this pit until the storms passes reducing pressure and volume in downstream pipes And ensures that this keeps happening and we get less of this But how is this saving the city? Little bit small no? That's why we use a whole ton more of them Many cities have hundreds scattered around and they come in all shapes and sizes Some retention ponds are more like retention lakes like this one in Tokyo that we’ll look at that later Others hold water year round like Saigon Park in Mississauga These are beautiful places that control floods in the same way as dry ponds except standing water helps filter out pollutants and sediments that wash in off the street Through the power of editing we’re at a much more basic pond but even this one has a secret feature that protects the neighborhood if it overflows And… it's right here where I’m standing doesn’t look like much but lets go higher And we’ll switch to technical drawings where we’ll see its labeled “Emergency Spillway” This area is lower and just like a spout on a measuring cup if the pond overflows water is directed downhill towards the nearby stream instead of homes This is called overland flow and it’s also designed as a failsafe for modern city streets when sewers overflow If we look at city engineering plans the large purple arrows show how roads are designed to convey water to places where the road sags and water is safely directed into nearby rivers or even golf course ponds This is known as the major system in stormwater design and part of the protections for newer neighborhoods and most retention ponds that you probably didn’t know existed But sometimes there’s not enough space for a pond and we need a different solution And it’s right here? Where is it? It’s actually down below and there are rows of buried tubes That are built using large interlinked chambers and can store stormwater underground You might notice the bottoms are not sealed and that’s on purpose to allow for a process called infiltration That lets rainwater seep into the ground which keeps this water out of the sewer and restores the natural flow back into the groundwater which is used by plants and for drinking water It’s also not just parks but many malls and commercial sites are required to install these systems And so it’s all around you! Sewer pipes, channels, dry ponds, wet ponds, dams! And by the 2000s Toronto and many other cities thought they knew how to predict rain knew how to build communities and keep them safe I know how to do it You know nothing Pakistan has had some of its worst flooding ever this year Scientists say climate change has made the disaster worse And all the time the question is whether flooding would be worse in the future I’m having a pool party in my own house Woooooooo Toronto has been hit with 8X more major storms than expected in the last 15 years The one in 2018 nearly overtopped the channel and caused extensive flooding elsewhere And we’re fighting back, expanding channels like this one Building more water storage and bigger sewers But it had me wondering what will the future look like as cities grow along with severe rain storms? Let’s delve into two different cities to see what the upgrades to this infrastructure might look like First up, Tokyo This city uses infrastructure to subjugate and control nature on a massive scale Lets go [Travel Youtuber Music] Our first stop is this apartment building at Tetsugakudo Park Heights The building doesn’t look that special It's another apartment located close to the river although the area is quite gorgeous But what if I told you that if you lived here and saw the rec area flooded not only is it fine — but expected Weird right? Not for residents here the building is designed as a retention pond When the river rises too high it's designed to flow over this wall which is lower than the surrounding embankment It then floods into the recreational complex and even under the building to capture excess water that might flood the neighborhood But what about the building? Will it be damaged? As we walk around you might notice something interesting There’s nothing underneath It’s on stilts and this keeps the building safe But why go to these extreme lengths? The answer is money and space Tokyo has 14 million people and it’s heavily urbanized Buildings are placed up against major rivers to make the most of the room available The danger is the rivers are above the height of the city which means Tokyo is one giant floodplain that can cause Tens of billions of dollars in damage and many deaths if the river overflows as it has in the past Tokyo’s government simulated the damage should an embankment break in a major area and it’s chaos subways flooded! Major neighbourhoods taken out Tokyo paralyzed! So they have to protect the city at all costs which include expensive and unusual retention ponds as one part of that strategy But what if you need more than a tennis court? A lot more This is Nissan Stadium and Shin Yokohama park which contains 6 large sports fields and rec areas spread across 1.4km and it's all designed to flood If we look from one end of the park it’s a giant basin and at full capacity can contain 3.9 billion liters of water The secret to making this work is this 200m dip in the berm that protects the city from the river In this up close shot you can clearly see how it’s been lowered And looking from the side we can see how water will stream across when the river becomes flooded into the outermost part of the park which is the easiest to clean up And if water keeps coming it’ll fill the rest of the complex Oh and how is the arena protected? With stilts of course! This is how high it flooded before and that won't cause any damage or interruptions even during a world rugby event But what about the buildings inside the park? I saw photos like this that showed them underwater. When you get close you'll see something unusual they have chonky windows and doors that are found on the ground floor of this entire building. Think ship doors You know the ones that keep them from sinking That’s it right here and these small details made me appreciate the thoughtfulness and multipurpose nature of this complex And Japan makes it easy to visit other pieces of infrastructure and I rather do that than visit the usual tourist sites There’s a place 56km north of the stadium that I really wanted to see (Panting)...It's there
This is the $2 Billion Metropolitan Area Outer Underground Discharge Channel and it captures water from five rivers and stores it in massive underground silos that each are big enough to hold the space shuttle or the statue of liberty We started the tour in the pressure regulating section and experiencing the scale of this facility was intense It’s nicknamed the temple for obvious reasons. Oh side note tons of movies and tv shows have been shot here and even Pharell has visited We were later taken to walk around one of the storage tanks and look down to see the section we were just in Here’s a person for scale and it looks so tiny up here I had a ton of fun and I could better understand how much goes into protecting Tokyo and why they would spend billions to do so These projects are working The stats for Tokyo show a huge drop in flooding over decades But the cost is enormous not only in billions spent but the destruction of the natural environment Nearly all the rivers through Tokyo have been paved over and many retention ponds are far from natural Is this the price for making bigger cities? But maybe the problem is that we fight nature and what if the solution is the opposite and we work with it instead? That takes us to this It’s a garden and it’s also a sponge It takes stormwater off the streets through this grate here Where it percolates through the soil holds and filters the water before releasing it The goal is to avoid expensive, centralized storage and instead use more and smaller infrastructure to keep rain out of sewers There are many types of these systems and if you build enough the city becomes a giant and beautiful sponge that rolls back the problems with urbanization This is called green infrastructure or low-impact development Today, many cities are green-curious but some like Philadelphia have delved in deep This map show an incredible 12 year effort hundreds of projects that cover 1700 acres They put green infrastructure everywhere including schools, roadsides and private land It beautifies the city of the Fresh Prince and more importantly fixed a major pollution issue for cheap saving billions of dollars Philadelphia had raw sewage being dumped into rivers during major storms and they were ordered to fix this Traditional grey infrastructure like the ones being built in London would have cost over $8 billion dollars Green infrastructure cost 75% less but at city-scales was unproven at the time It’s a risk that paid off for Philadelphia I would need a full video to explain all of this as water quality is a huge part of stormwater management As to flooding reduction Philadelphia hasn’t published any stats except the billions kept out of waterways Other cities are investing heavily in green infrastructure but it’s just the beginning as this technology is starting to be widely adopted Heavier rain is coming to all our cities and I can’t tell you if yours will go down the Grey Tokyo or the Green Philadelphia path probably a combination of both Subscribe if you want more in-depth explainers Just like this one that help you appreciate the world around you If you want to support the channel consider Brilliant I think they’re a great learning resource Thanks and see you in the next one Bye